Testosterone secretion is the net result of intratesticular testosterone biosynthesis, degradation and finally, its release into the testicular vasculature. While considerable information is available regarding testosterone biosynthesis, little is known about intratesticular testosterone degradation. Moreover, nothing is known about the effect of testicularly versus peripherally derived testosterone metabolites upon gonadal steroid sensitive tissues either within the testis or in the periphery of the male. In comparison to our knowledge of the cellular secretion of proteinaceous molecules virtually nothing is known about the mechanism by which steroids are released into the vasculature of the steroid secreting organ. The testis is no exception to this rule. The continued development of the rabbit testis perfused in vitro with an artificial medium suggests that this system may be the most realistic one to completely examine the factors regulating androgen secretion by a mammalian testis. We will utilize this technique to investigate the secretion and biological activity of testicularly derived testosterone metabolites such as dihydrotestosterone and estrogens; the mechanism by which testosterone escapes into the testicular vasculature from the steroidogenic cell and the potential regulatory effects of testicular steroids upon testosterone secretion.